1. Field
This specification relates to an apparatus supplied with driving power from a battery, for example, a mobile telephone terminal, etc., a method of protecting a battery used for the apparatus, and program.
2. Description of the Related Art
A mobile terminal, such as a mobile telephone terminal, etc., is driven by a battery. FIG. 13 illustrates an example of a configuration for charging a battery, by an AC adapter, for use as a driving power source of a mobile telephone terminal, for example.
A terminal function section 100 has a control section including a CPU, a wireless communication section, an operation section, a display section, a microphone, a speaker, etc. The terminal function section 100 is a part which functions as a mobile telephone terminal, and is supplied with driving power by a battery 11 to be driven.
As a charging circuit 20, a circuit including a protection circuit 21, a charge control IC (integrated circuit) 22, an FET (field-effect transistor) 23, a current detection resistor 24, a charge display LED (light-emitting diode) 25, and a current restriction resistor 26 is connected to the battery 11.
At charging time by the AC adapter 200, a charging current flows from the AC adapter 200 to the battery 11 through a protection circuit 21, an FET 23, and a current detection resistor 24 to charge the battery 11. The protection circuit 21 is a circuit which prevents a current from flowing from the battery 11 to the AC adapter 200.
In this manner, a battery is normally used in a mobile terminal (mobile electronic device), such as a mobile telephone terminal, for example. And there are various kinds of batteries, and the batteries have different operating temperature ranges and operating voltage ranges.
Referring to an operating temperature range, a lead-acid battery has a range of −10° C. to +40° C., a nickel-cadmium battery has a range of −20° C. to +45° C., a nickel-hydrogen battery has a range not exceeding +40° C., and a lithium-ion battery has a range of −10° C. to +40° C.
Also, referring to an operating voltage range, a lead-acid battery has a range of 1.8 V to 2.1 V, a nickel-cadmium battery has an operating voltage of 1.2 V, a nickel-hydrogen battery has a range of 1.1 V to 1.4 V, and a lithium-ion battery has a range of 3.0 V to 4.2 V.
A lithium-ion battery is used for various kinds of mobile terminals, such as a mobile telephone terminal as a battery having a relatively wide operating temperature range, having little current self-leakage, and being capable of supplying a relatively high driving voltage stably at use time.
In the case of the lithium-ion battery, if the battery is charged at a high temperature of 50° C. or more, deterioration of the battery becomes significant. However, the battery has a characteristic in which deterioration of the battery can be prevented by lowering the battery voltage to a predetermined level (for example, about 3.6 V).
In recent years, it is thought that a battery of a mobile terminal, such as a mobile telephone terminal, etc., is charged by a solar cell from the viewpoint of ecology, etc. Accordingly, it is thought that a mobile terminal is equipped with a solar cell, and the mobile terminal may be left on a sunny spot, etc.
Thus, Japanese Unexamined Patent Application Publication No. 7-250437 has disclosed an invention of a power-source unit in which if a charging voltage of a battery, which is a lithium-ion battery, reaches a first predetermined level (for example, 4V), the charging voltage is decreased to a second predetermined level (for example, 3.6 V).
In the invention disclosed in Japanese Unexamined Patent Application Publication No. 7-250437, discharging is performed in a highly-illuminated environment having a large output power from a solar cell. Accordingly, it can be expected that deterioration of a battery will be effectively restrained by applying the invention disclosed in Japanese Unexamined Patent Application Publication No. 7-250437 to various kinds of devices in which the battery is charged by a solar cell.
However, a temperature of a battery mounted on a terminal apparatus, such as a mobile telephone terminal, etc., increases not only in the case of a mobile terminal equipped with a solar cell. There are cases where a mobile terminal which is not equipped with a solar cell is left on a sunny spot near a window, etc. Thus, it is necessary to allow restraining the battery from deteriorating in various kinds of mobile terminals equipped with a battery regardless of a solar cell.
Also, in the case of the invention described in Japanese Unexamined Patent Application Publication No. 7-250437, if a charging voltage of the battery (charging battery) has reached a predetermined first level in a highly-illuminated environment having a large output power from a solar cell, discharge is carried out to a predetermined second level.
Accordingly, it is thought that even if the battery has not become high temperature, when the charging voltage becomes the first level, discharge is sometimes carried out. In this case, unnecessary discharge is carried out, and thus there is an increasing possibility that necessary power is not supplied from the battery at necessary time.
On the contrary, it is thought that there are cases where regardless of the battery having a high temperature, since the charging voltage of the charging battery has not become the first level, discharge is not carried out while the battery is kept to have a relatively high charging voltage. In this case, it is thought that there are cases where discharge is not carried out at adequate timing, and thus it is not possible to sufficiently restrain deterioration of the battery.
In view of the above points, it is desirable to reliably and adequately restrain deterioration of a battery which is mounted on various kinds of mobile terminal in order to supply driving power.